1. Field of the Invention
The present invention relates to an electron source having a plurality of electron-emitting devices and an image display apparatus using the electron source.
2. Description of the Related Art
Electron-emitting devices include field emission and surface conduction electron-emitting devices. A conventional surface conduction electron-emitting device and manufacturing steps thereof are described with reference to FIGS. 16A, 16B and 17A to 17D.
A pair of electrodes 2 and 3 is provided on a substrate 1 (FIG. 17A). The electrodes 2 and 3 are connected by a conductive film 4 (FIG. 17B). A voltage is applied between the pair of electrodes 2 and 3 so that a first gap 7 is formed partially on the conductive film 4 (FIG. 17C). Specifically, an electric current is applied to the conductive film 4 so that Joule heat is generated. The first gap 7 is formed partially on the conductive film 4 with the Joule heat. This process is called energization forming (process). A pair of conductive films 4a and 4b which is opposed to each other via the first gap 7 is formed by the energization forming process. The device is subject to a process that is called an (energization) activating process. The energization activating process is a process for applying a voltage between the pair of electrodes 2 and 3 in a carbon-contained gas atmosphere. As a result, conductive carbon films 21a and 21b can be formed on the conductive films 4a and 4b near the first gap 7 (FIG. 17D). Further, a second gap narrower than the first gap 7 is formed by the carbon films 21a and 21b. The electron-emitting device is formed through the above steps.
FIG. 16A is a plan view schematically illustrating the electron-emitting device which is subject to the energization activating process. FIG. 16B is a cross-sectional view schematically illustrating a cross section taken along line B-B′ of FIG. 16A. In FIGS. 16A and 16B, the same members as those shown in FIGS. 17A to 17D are denoted by the same numbers as those in FIGS. 17A to 17D. In order to allow the electron-emitting device to emit electrons, an electric potential to be applied to one of the electrodes 2 and 3 may be made to be higher than that to be applied to the other electrode. When the voltage is applied to the electrodes 2 and 3 in such a manner, a strong electric field is generated near the second gap 8. As a result, the electrons pass trough a portion, which is an edge of the carbon film (carbon film 21a or 21b) to be connected to the electrode on the low-potential side of the electrodes 2 and 3 and is an outer edge of the second gap, into the outside (namely, the electrons are emitted).
Japanese Patent Application Laid-Open No. 2002-352699 discloses an electron-emitting device, which is provided with a plurality of conductive films electrically connected to each other in parallel, between the pair of electrodes 2 and 3 (a plurality of conductive films having an electron emitting portion, respectively). Such a configuration can reduce probability of breaking the device due to occurrence of accidental discharge (electron discharge). Specifically, in the electron-emitting device having one conductive film, when the conductive film is broken due to discharge or the like, the device loses the electron emitting function. However, when the electron-emitting device has a plurality of conductive films described above, the device does not lose the electron emitting function unless all the conductive films are broken.
The electron emitting portion can be used for an electron source and an image display apparatus. For example, a plurality of electron-emitting devices is arranged on the substrate, so that an electron source can be configured. Further, an image display apparatus can be configured with an electron-emitting device and a substrate having a light emitting film composed of a phosphor.
Such an image display apparatus is demanded to reduce a fluctuation in luminance for a long period and display a video stably. For this reason, in such an image display apparatus, a variation of an electron emission characteristic among the electron-emitting devices are demanded to be small, and the electron-emitting devices are demanded to be capable of maintaining the electron emission characteristic for a long period (even when the devices are used for a long period, the change in the electron emission characteristic is small).
In order to reduce the variation in the electron emission characteristic among the electron-emitting devices, the following method can be provided. In this method, the plurality of conductive films electrically connected to each other in parallel is formed between the pair of electrodes, and the electron emitting portions are provided to the plurality of conductive films, respectively. In such a configuration, since the plurality of conductive films is electrically connected in parallel, the electron emission characteristic of one device becomes an average of the electron emitting properties of the respective conductive films. As a result, the variation in the electron emission characteristic among the electron-emitting devices can be reduced.